(1) Field of the Invention
The present invention relates to check or plate valves and particularly to minimizing pressure losses in one-way flow control valve assemblies. More specifically this invention is directed to check or plate valves and especially to such valves for use in reciprocating compressors. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
(2) Description of the Prior Art
Check or one-way flow control valves employing annular plates as the moving element or valve member are well known in the art. An example of such a prior art "plate" valve is shown in U.S. Pat. No. 3,656,500. Valves of the type disclosed in U.S. Pat. No. 3,656,500 find wide utility and, for example, are employed in both the inlets to and discharge lines from reciprocating compressors. In a typical reciprocating type compressor installation, there will be from two to sixteen valves per cylinder and thus a single compressor may have in excess of one hundred plate valves associated therewith. A failure of any one valve or movable plate will disable the entire compressor. Accordingly, reliability is a primary consideration in the design of a plate valve.
To briefly describe prior art plates valves of the type exemplified by U.S. Pat. No. 3,656,500, such devices have a seat member with a plurality of passages or ports therethrough. These passages or ports are of arcuate shape and are arranged in concentric circles to thereby effectively define a plurality of annular inlet ports to the valve chamber or chambers. A guard member faces the seat member and is also provided with through passsages or ports which effectively define a plurality of concentric, annular discharge passages or ports in the valve. The discharge passages are at the opposite side of the valve chamber from the inlets and are radially displaced, i.e., staggered with respect to the inlet. The guard member is also provided with a plurality of recesses which receive biasing springs. Annular plate or valve members, in the form of metallic or nonmetallic sealing strips, are located in the valve chamber intermediate the seat and guard. These sealing strips or plates, which have a width exceeding the width of the ends of the inlet ports, are constrained so as to be in alignment with the inlet ports. The plates are resiliently biased, by means of the aforementioned springs, against the seat whereby the valve will be normally closed. When the forces on the plates resulting from the applied pressure exceed the spring bias, the plates will move away from the seat and fluid may flow through the valve from the valve inlet passages to the valve discharge passages. Since there is an offset of the discharge passages with respect to the inlets, there is a change in direction of flow of the fluid as it passes through the valve.
While generally having adequate reliability, prior art plate valves have been characterized by comparatively large pressure losses. These pressure losses reduce the efficiency of compression and, if a given output pressure is required, the energy input to the compressor must be increased sufficiently to compensate for the losses. The problem of pressure losses is particularly acute in the case of compressors operating at low overall pressure ratios; i.e., pressure ratios in the range of 1.5-2.5/l. Compressors employed on natural gas pipelines are characterized by a low overall pressure ratio and it is of critical importance to minimize the energy consumption of such compressors incident to delivery of the gas under pressure to the consumer, especially when such compressors are powered by the very gas they are compressing.
It has, in the prior art, been universally believed that pressure losses in plate valves primarily occur at the seat area. Accordingly, in an effort to minimize such losses, it has previously been common practice to enlarge the seat area at the expense of the area between the annular plates. Thus, prior art plate valves have been characterized by sealing rings or plates having a width which was large when compared to the spaces between the rings. In a typical prior art plate valve the ratio of the sum of the seat areas (.SIGMA.Fs) to the sum of the areas between the plates (.SIGMA.Fb) (i.e. .SIGMA.Fs/.SIGMA.Fb) was 1.2. A further characteristic of prior art plate valves was that the sealing rings or plates were typically of equal width and, because of the above-discussed effort to minimize seat losses while ignoring any other losses, the rings were closely spaced. Also, prior plate valves intended for use in compressors operating at comparatively high speeds, i.e., compressors operated at 800-900 rpm, were designed with a lift which did not exceed 0.100 inches, since it has been generally considered that valves with lift exceeding 0.100 inches would not be reliable.